The performance of an internal combustion engine can be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one of such camshafts is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other of such camshafts is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts can be driven by a single crankshaft powered chain drive or belt drive. A crankshaft can take power from the pistons to drive at least one transmission and at least one camshaft. Engine performance in an engine with dual camshafts can be further improved, in terms of idle quality, fuel economy, reduced emissions or increased torque, by changing the positional relationship of one of the camshafts, usually the camshaft which operates the intake valves of the engine, relative to the other camshaft and relative to the crankshaft, to thereby vary the timing of the engine in terms of the operation of intake valves relative to its exhaust valves or in terms of the operation of its valves relative to the position of the crankshaft.
As is conventional in the art, there can be one or more camshafts per engine. A camshaft can be driven by a belt, or a chain, or one or more gears, or another camshaft. One or more lobes can exist on a camshaft to push on one or more valves. A multiple camshaft engine typically has one camshaft for exhaust valves, one camshaft for intake valves. A “V” type engine usually has two camshafts (one for each bank) or four camshafts (intake and exhaust for each bank).
Variable camshaft timing (VCT) devices are generally known in the art, such as U.S. Pat. No. 5,002,023; U.S. Pat. No. 5,107,804; U.S. Pat. No. 5,172,659; U.S. Pat. No. 5,184,578; U.S. Pat. No. 5,289,805; U.S. Pat. No. 5,361,735; U.S. Pat. No. 5,497,738; U.S. Pat. No. 5,657,725; U.S. Pat. No. 6,247,434; U.S. Pat. No. 6,250,265; U.S. Pat. No. 6,263,846; U.S. Pat. No. 6,311,655; U.S. Pat. No. 6,374,787; and U.S. Pat. No. 6,477,999. Each of these prior known patents appears to be suitable for its intended purpose. However, it would be desirable to allow a check valve in spool cam torque actuated (CTA) phaser to lock somewhere along a path of travel, other than at either end stop limit of travel.